diff --git a/mongoose.h b/mongoose.h
index fc00967b..9c9f8ab8 100644
--- a/mongoose.h
+++ b/mongoose.h
@@ -330,6 +330,9 @@ struct timeval {
 #include <stdlib.h>
 #include <string.h>
 #include <time.h>
+
+#include <pico/stdlib.h>
+int mkdir(const char *, mode_t);
 #endif
 
 
diff --git a/src/arch_rp2040.h b/src/arch_rp2040.h
index 5511c66e..ace069bf 100644
--- a/src/arch_rp2040.h
+++ b/src/arch_rp2040.h
@@ -9,4 +9,7 @@
 #include <stdlib.h>
 #include <string.h>
 #include <time.h>
+
+#include <pico/stdlib.h>
+int mkdir(const char *, mode_t);
 #endif